Nematic liquid crystal materials are finding wide use in display devices such as watch faces. One difficulty with conventional nematic liquid crystal devices is that they depend on the ambient light for illumination and often exhibit poor contrast under bright illumination. Therefore, it is highly desirable to develop liquid crystal compositions which give a high contrast with the surroundings when the liquid crystal changes phase or orientation.
Articles relating to the study of fluorescent solutes in liquid crystal solvents include:
1. E. Sachman, et al., J. Am. Chem. Soc. 90, 3569 (1968); PA0 2. E. Sachman, et al., Chem. Phys. Letters 4, 537 (1970); PA0 3. G. Baur, et al., J. Appl. Phys. 44, 1905 (1973); PA0 4. H. Beens, et al., Chem. Phys. Letters 8, 341 (1970); and PA0 5. R. D. Larrabee, RCA Review 34, 329 (1973).
Liquid crystals have also been used as anisotropic solvents to orient pleochroic nonfluorescent guest molecules and control their visible light absorption, see G. H. Heilmeier, et al., Mol. Cryst. and Cryst. 8, 293 (1969).
The use of a fluorescent material whose fluorescence is dependent on the phase or orientation of the liquid crystal could provide the high visual contrast desired in liquid crystal displays and devices. However, the interaction between liquid crystal materials and dissolved fluorescent solutes currently is not susceptible to delineation so that successful liquid crystal/fluorescent material combinations can be predicted. Therefore, it is highly desirable to develop such combinations which can be used in liquid crystal devices and displays.